After failing on the land, the Bermans moved to Sioux City, Iowa, where David got his start as a mobster. At the age of 13, he ran a crew of teenaged thugs committing petty shakedowns and eventually a string of illegal distilleries. He then went on to run his own bank-robbing crew. After developing close ties to the Genovese crime family, he moved to Minneapolis, Minnesota, where he operated a major bookmaking operation in rivalry with local mob bosses Kid Cann and Tommy Banks. One of Berman's closest enforcers during those years was Israel "Ice Pick Willie" Alderman, a homicidal Jewish gangster from North Minneapolis. His brother, "Chickie" Berman, also worked for him.

Due to his close relationship with Minneapolis mayor Marvin L. Kline, Berman briefly eclipsed his rivals as boss of the Minneapolis gambling rackets.

According to his daughter, Susan, Berman also used his crew to intimidate and terrorize members of the pro-Nazi Silver Shirts, driving them out of Minneapolis.

Persecution of his fellow Jews enraged Berman so much that he enlisted in the Canadian Army. He had previously been turned away by the U.S. military as a convicted felon. In addition, Pearl Harbor had not yet brought the U.S. into World War II. He saw combat in the European Theater with the 18th Armoured Car Regiment (12th Manitoba Dragoons), a reconnaissance outfit, along with Minnesota friend Nathan Gittlewich. Berman was well liked, and fellow troopers did not know of his criminal background.

After his return to Minneapolis, Davie's gambling operations were shattered during the first term of racket busting Mayor Hubert Humphrey. Berman moved his crew to Las Vegas and operated there in concert with Genovese Family associate Moe Sedway,

Almost immediately after the 1947 assassination of Bugsy Siegel, Sedway and Berman walked into the lobby of the The Flamingo and announced that they were in charge. Berman died on the operating table during surgery to remove polyps from his colon on Father's Day, 1957.

While he lived in Minneapolis, Berman met and married Gladys Ewald, a German-American dancer who later converted to Judaism. The couple's only child, daughter Susan Berman, wrote a memoir about growing up as Las Vegas mob royalty titled Easy Street (1981, '83). In her memoir, Susan indicates she knew little of her father's past until an acquaintance brought to her attention the mentions of her father in the book The Green Felt Jungle. Gladys Berman died shortly after Davie Berman at age 39 of an overdose of barbiturates, although it is unclear whether it was suicide.